Physiologic electrode tablet



June 16, 1964 0. PHlPPS ETAL 3,137,291-

PHYSIOLOGIC ELECTRODE TABLET Filed Aug. 28, 1962 Fig.

20,000 POUNDS INVENTORS CLIFFORD G. PHIPPS GEORGE G. LUCCHINA UnitedStates Patent 3,137,291 PHYSIOLOGIC ELECTRODE TABLET Cliiford G. Phipps,Newbury Park, and George G. Lucchina, Oxnard, Calif, assignors to theUnited States of America as represented by the Secretary of the NavyFiled Aug. 28, 1962, Ser. No. 220,102 2 Claims. (Cl. 128-2.1) (Grantedunder Title 35, US. Code (1952), see. 266) The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

The invention relates to medical instrumentation, and more particularlyto the composition of an electrode tablet and the method of fabrication.

In US. patent application Serial No. 181,214, having a commonco-inventor with the present application, there is described a uniquephysiologic electrode package comprising a plurality of cork discs forsupporting a metallic pellet in fixed spaced relation to the skin of thewearer. A compatible electrolytic gel provides the conductive electricalbridge between the pellet and the skin. The present invention isdirected to the composition and method of making the metallic pelletused in the above described electrode package, although not limitedthereto.

The electrode package functions to intercept the minute bio-electricvoltages at the body surfaces, and makes them available foramplification and processing into useable clinical records.Specifically, the metallic tablet, being an integral part of theelectrode package allows the interception of the desired coherent A.C.voltages without the unwanted random D.C. voltages which are usuallycoexistent. Such D.C. potentials are generated between the inner facejunctions, or couples, of the pellet/ gel and gel/ skin surfaces andaffect the quality of the recording. These D.C. voltages are a functionof the electromotive series of the metals employed, the ionicdescription of the gels employed plus other relatively minor factorsincluding temperature, humidity and ionizing radiation.

Another important electrical characteristic is the skin/ electroderesistance. Low values are desirable to minimize the resistancemodulation of the driven amplifier in the recording system.

One of the more important physical characteristics of the metallicpellet is longevity to handling and use.

A careful laboratory evaluation of the prior art electrodes disclosedexcessive contact potentials and resistances which degrade the clinicalrecords. The use of deposited filrn electrode tablets were found to bedeficient from the standpoint of high resistance value, as well aslongevity since the coatings have a tendency to rub off with use andhandling.

The disadvantages of the prior art electrodes have been avoided byfabricating an electrode from a selected ratio of Ag and AgCl by weight,which mixture is finely divided and uniformly mixed. With the leadconductor suitably positioned, the desired amount of the mixture isinserted in a stainless steel die, and by means of a hydraulic press apressure in the order of 20,000 lbs/sq. inch is applied to the mixturefor approximately a minute. The high pressure achieves an intimatebonding between the two ingredients without the need for a binder.

An electrode made by this process achieves the desired characteristicsnamely low resistance, low contact potential and good longevity.

An important object of this invention is to provide a physiologicelectrode tablet that will enable improved recordings of bio-electricvoltages.

Another object is to provide such a tablet that will intercept coherentA.C. voltages without the unwanted random D.C. voltages.

3,137,291 Patented June 16, 1964 Still other objects are to provide anelectrode which is more rugged in construction; has a longer life; andis relatively inexpensive in cost.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a schematic representation of the steps in the method ofmanufacturing the novel electrode tablet; and

FIG. 2 is a plan View of the electrode tablet.

Referring to the drawing where like reference numerals refer to similarparts there is shown in the lower end of FIG. 1 a physiologic electrodetablet 10 having imbedded therein a conductor 12 and manufactured in thefollowing manner. Tablet 10 comprises a mixture of silver (Ag) andsilver chloride (AgCl).

It has been found that the following specification for the mixture withregard to the impurities in the two ingredients has given good results:

Conductor 12 can be a fine grade Wire Ag #20 AWG or tinned Cu #20 AWG.In carrying out the method the following steps are taken:

(1) Weigh out the selected ratio of Ag and AgCl by scales 14.

For purposes of this example, a ratio of 30% finely ground Ag and 70%finely ground AgCl is used.

The effects of other ratios of Ag and AgCl wil be hereinafter discussedwith reference Table No. 1.

(2) Pulverize AgCl to as fine a powder as possible in a porcelain motar16.

(3) Add Ag to AgCl and mix throughly approximately for 5 minutes oruntil mixture appears to have uniformity. It should be noted that toavoid discoloration of the pellet, it is advisable to conduct allweighing in darkness or altificial light, and to keep the mixturecovered whenever possible.

(4) Place bared end of conductor 12 in die 18.

(5) Insert the necessary amount of mixture in die 18, which is made ofstainless steel. For a pellet of 9 mm. in diameter and 2 mm. inthickness approximately 1.2 grams of the mixture is used.

(6) Place die 18 in a hydraulic press 20 and apply a pressure in theorder of 20,000 lbs./ sq. inch.

(7) Hold pressure in die for a duration of 30 to 60 seconds.

(8) Remove electrode pellet from die and trim away any excess material.

(9) Remove all traces of the mixture from the die since it is verycorrosive to metal.

The precise phenomena which occurs between the fine divided Ag and AgClingredients when subjected to the high pressure in the order of 20,000lbs./sq. inch or greater is not fully understood. It is believed thatthe two ingredients ionically act as a liquid under the high pressure toachieve an intimacy not otherwise obtainable. It is well known that Agis a very good conductor, and that AgCl is a very poor conductor.However, the combination when subjected to such high pressure causes thecombination to give desired results, namely, low D.C. lead potentialsand high conductance.

As noted therefor, some fifteen dilferent ratios of Ag to AgCl wereexamined to determined their pertinent electrical characteristics ofresistance and potential. The test was conducted in amanner whicheliminated skin resist- .ance and the skin/ gel couple. The resultsappear in the following Table No. 1:

Table No. 1.Electrical Characteristics of Electrodes Varying in Ratio ofAg t AgCl Resistance E.M.F. in

Ag/AgCl by Weight in ojlms,

As will be observed from Chart No. 1, the 100% Ag generated anunacceptable contact potential, whereas the high ratios of AgCl to Agresulted in prohibitively high resistances. Between these limits,excluding about six combinations which are marginal, five ratios appearidentical. The mechanical strength of these five tablets withthe'identical electrical characteristics, as well as longevityMillivolts contains less than one-half the amount of silver of the 70/30tablet and thus the 30/7O tablet is the obvious choice. 7 t

The instant invention provides a novel composition and method ofmanufacturing an electrode tablet thatis particularly suitable forelectroencephalograph and electro cardiograph devices both from-anelectrical and physicall consideration, as well as cost and comfort tothe user.'

'Obviously many' modifications and variations of the present'inventio nare possible in the light of the above.

teachings. It is therefore to be understood that within the scope of theappendedzclairns the invention may be practiced otherwise thanjasspecifically described.

We claim:

1. Aphysiological electrode tablet for electrical contact I with apersons skin through an electrolytic gel for recording the ionic energyin the body with a minimum of 0on tact potential, which electrodecontains an intimately bonded homogeneous mixture of only finely dividedAg and AgCl selected from a range of the ratios between 30% Ag to 70AgCl and 70% Ag to 30 AgC l.

2. The tablet of clairn 1 wherein a silver wire con- Y ductor isintegrally embedded therein.

characteristics, were so similarrthat the only cons'idera-f tion thatremained was a matter of cost. The 30/70 tablet References "Cited in thefile of this patent UNITEDVSTATES PATENTS 2,654,795 r Brill et a1. 7Oct. 6, 1953 2,654,945 Richardson et al Oct. 13, 1953 2,729,559Matsukawa -Jan.'3, 1956 2,895,479

1. A PHYSIOLOGICAL ELECTRODE TABLET FOR ELECTRICAL CONTACT WITH A PERSON''S SKIN THROUGH AN ELECTROLYTIC GEL FOR RECORDING THE IONIC ENERGY IN THE BODY WITH A MINIMUM OF CONTACT POTENTIAL, WHICH ELECTRODE CONTAINS AN INTIMATELY BONDED HOMOGENOUS MIXTURE OF ONLY FINELY DIVIDED AG AND AGCL SELECTED FROM A RANGE OF THE RATIOS BETWEEN 30% AG TO 70 AGCL AND 70% AG TO 30 AGCL. 